Various manufacturing processes involve winding of filaments or roving onto manufactured articles. The need for higher winding speeds, more consistent winding operations from part to part, and the complexity of the shapes onto which the filament or roving is to be wound have contributed to the need for more accurate control over the tension of the filament or roving.
In the past, filament tension control has been accomplished by textile-type tensioners which have been found poorly suited to achieve the above-noted objects. In particular, these types of tensioners do not allow bidirectional control of filament tension, and hence there is not compensation for high filament accelerations.
Hydraulic motor tensioning systems have been found to function quite well in these applications; however, they are quite costly, difficult to install and, due to the hydraulic supply and connecting lines, highly immobile.
One prior attempt to overcome the above limitations involved the use of a microprocessor to control a permanent magnet DC motor by means of pulse width modulation techniques. This tension control system utilized filament tension sensing apparatus, such as a gray code encoder, potentiometer or other position transducer to sense the tension in the filament and to develop a signal representative of same. This signal was coupled to the microprocessor which operated a pulse width modulator and transistor bridge circuitry to in turn control the torque of the motor and hence the tension in the filament.
The tension sensing apparatus included a roller engaged by the filament, the roller being movable along a linear path with the tension in the filament determining the position of the roller along the linear path. The roller was in turn coupled to a wire rope and spring with the wire rope engaging the transducer to cause an actuator thereof to rotate as the roller moved along the linear path. An indication of filament tension was thereby obtained at the output of the transducer.
This system also included means for detecting breakage of the filament which included means for detecting when the position transducer output indicated filament tension outside of a predetermined range on either side of a set point. If such an event occurred the motor was de-energized to allow the situation to be rectified.
It was found that the microprocessor-based system described above was overly large and expensive.
Furthermore, the means for detecting filament breakage operated in a less than optimal fashion. In particular, the set point could be adjusted to a relatively low level which would in turn prevent motor deenergization even if filament tension dropped to zero. Furthermore, there was no means to prevent motor shutoff in the event of a relatively short tension excursion. Finally, particularly in situations where the filament was guided by pulleys or other guiding apparatus through a resin impregnation bath and then onto the article, if filament breakage occurred in the vicinity of the article, the tensioner motor would reverse and operate at near maximum speed against the friction introduced by the guiding apparatus and bath in an attempt to maintain filament tension at the desired value. This action would cause the impregnated filament to be wound back onto the non-impregnated filament before the motor is stopped.